Date Added: May 2012
Cognitive Radio Networks (CRN) has attracted great attention recently as a means to resolve the critical spectrum shortage problem. With Dynamic Spectrum Access (DSA) techniques, CRN can be granted access of spectrum secondarily, i.e., as long as it can guarantee no interference to any Primary User (PU) who is using this spectrum at this time in this location. This means that the cognitive radios have to periodically sense the spectrum to detect the primary user's activity. They have to vacate the channel immediately whenever PU activity is detected.